Land Mobile Radio (LMR) systems are deployed by organizations requiring instant communication between geographically dispersed and mobile personnel. Typical users of LMR systems include police departments, fire departments, medical personnel, security personnel, EMS, and the military.
Current LMR systems can be configured to provide for radio communications between one or more sites and subscriber radio units in the field. A subscriber radio unit (hereinafter “radio”) may be a mobile unit or a portable unit. LMR systems can be as simple as two radio units communicating between themselves and a site over preset channels, or they can be complex systems that include hundreds of radio units and multiple sites.
LMR systems can be broadly divided into two classes: (1) trunking LMR systems; and (2) conventional LMR systems. A trunking system generally includes one or more trunking sites and dispatch control centers. FIG. 1 illustrates a typical trunking LMR system 100 including a trunking site 104 and a dispatcher 108. The trunking site 104 includes a control channel 112 and one or more traffic channels (e.g., 116, 118). Typically a group of radio users (e.g., 124, 128) create a user group to communicate with each other and the dispatcher 108. In a trunking system 100 there can be multiple radio users and multiple user groups.
Trunking systems streamline usage of Radio Frequency (RF) resources (e.g., traffic channels) through the use of mobility management. Mobility management allows the system to send periodic messages to the radios through a dedicated radio frequency base station, also known as a control channel, while the radios communicate back with the system. Said periodic messages may indicate coverage availability, signal strength, and other data to the radio, while communication from the radio may indicate to the system the radio's location and interested user group. If the radio stops receiving the messages from the control channel 112, the radio notifies the user, typically through visual and audible indicators, that the radio is outside of the coverage zone of the trunking system.
Mobility management allows dynamic routing of “Push-to-Talk” user group calls based on user availability in different geographic locations. Therefore, trunking systems implement mobility management to allow a radio unit to move from one geographic region to another while the system keeps track of the unit's location and user group affiliation within the unit's current geographic region. When a radio user wants to contact other radio users or a dispatcher in the same user group, the radio user sends a request to a trunking site controller 132 through the control channel 112. The trunking site controller 132 contacts the other trunking sites interested in the same user group. The trunking site controller in each interested site allocates an available traffic channel. Once a channel is available, the radio users in the user group are notified through the control channel, and their radios are placed in communication with the appropriate traffic channel to communicate with each other. Since a traffic channel is allocated dynamically on a per call basis, a trunking system provides efficient utilization of available bandwidth and RF resources.
Although trunking systems provide efficient usage of RF resources, it is achieved at significant costs. Specifically, the control channel required to provide communication of user location from the radios to the system is expensive. When cost is of concern, a conventional LMR system may be a preferred solution since the conventional system lacks the expensive control channel.
A conventional system allows the radio users to directly access a traffic channel, if available, and originate voice communication. FIG. 2 illustrates a conventional LMR system 200. Like the trunking system 100, the conventional LMR system 200 may include one or more conventional sites, although only one conventional site 204 and dispatcher 208 is shown in FIG. 2. However, unlike the trunking site 104, the conventional site 204 does not include a control channel. The conventional site 204 includes one or more traffic channels (e.g., 216, 220 and 224) each traffic channel being typically assigned to one or more user groups for use by radios, such as radio 228 and radio 232. The members of a user group may communicate with each other on the same traffic channel, thus allowing the users and the dispatcher to instantly communicate with each other without waiting for the system to allocate a traffic channel.
Although a conventional system may be more economical, one of its disadvantages is that the absence of a control channel precludes the system from sending periodic coverage indication messages to the radios, and the radios are unable to inform the system of its location or interested user group—features typically associated with mobility management as discussed above. Therefore, the system is unable to intelligently route originating traffic to select destination sites based on user availability, and the radio is unable to indicate to the user that the radio is outside of the coverage zone of the conventional system. As a result, a conventional system implements preconfigured routing to route the call from the originating radio to a fixed set of geographic locations, regardless of user availability in those sites. Accordingly, RF resources are typically wasted or inefficiently allocated when a user is not available in a site. While a conventional system may provide an initial lower cost LMR system solution, the lack of mobility-based routing and out-of-coverage indication limits the usage and capabilities of the system.